1. Field of the Invention
The present invention relates to a toner transport method and toner transport device for moving the toner on the surface of an electrostatic toner transporting device relative to the surface thereof by means of electrostatic force. The present invention also relates to a developing device, process unit, image-forming device, and image-forming method that use the aforementioned toner transport method.
2. Description of the Related Art
The devices disclosed in Japanese Laid-open Patent Application Nos. H9-197781 and H9-329947 are known as conventional examples of a copier, facsimile device, printer, or other image-forming device. In these image-forming devices, toner that is supported on a developing roller or other developer carrier with a moving surface is transported to a development position opposite from a photoreceptor or other latent image carrier, and the electrostatic latent image on the latent image carrier is developed. In this arrangement, the toner sometimes rubs between the developer carrier with the moving surface and the latent image carrier, bonds to either of the surfaces, and adversely affects the image. The toner is supposed to be moved electrostatically at the development position by the electrical potential difference between the surface of the developer carrier and the electrostatic latent image on the latent image carrier, but this electrical potential difference must be fairly large. This is because a force must be imparted to the toner prior to the start of electrostatic movement that is sufficient to overcome the adhesive force of the toner to the developer carrier that results from van der Waals forces, image forces, or the like, and this requires a large electrostatic force.
On the other hand, the device disclosed in Japanese Laid-open Patent Application No. 2002-341656, for example, is known as an image-forming device for developing a toner image without the use of a developer carrier with a moving surface. The developing device of this image-forming device utilizes the EH (Electrostatic Transport and Hopping) effect on the surface of an electrostatic toner transport substrate provided with a plurality of electrodes arranged at a prescribed pitch to transport the toner to the development position. This “EH effect” is an effect whereby the energy of a phase-shifted electric field acting on the grains is converted into mechanical energy, and the grains themselves move dynamically. The toner in which the EH effect occurs jumps with a forward-directed component by means of the phase-shifted electric field on the surface of the electrostatic transport substrate, and movement (transport) in the direction of the substrate surface and movement (hopping) in the direction perpendicular to the substrate surface are performed. Development with an extraordinarily low electrical potential can be achieved in a configuration that uses a developer carrier with a moving surface by transporting toner on an electrostatic toner transport substrate to the development position while causing the toner to hop. For example, it is also possible to selectively affix toner to an electrostatic latent image in which the potential difference from that of the surrounding blank portions is only a few dozen volts.
However, the developing device of this image-forming device is unable to adequately supply charged toner to the electrostatic toner transport substrate, and there is a risk of adverse effects due to deficient charging of the toner. Specifically, the toner is charged as it is rubbed by the rotation of the agitator inside the toner hopper, drawn up from the toner hopper to the surface of an electrostatic roller, and rubbed by a regulating blade, but this amount of friction can be inadequate.
Therefore, the four inventors are developing a new toner feeding device for feeding toner to an electrostatic toner transport substrate after adequately friction-charging the toner by mixing the toner with glass beads or other friction-facilitating particles made up of a substance that promotes friction, and agitating the toner while in this mixture. This toner feeding device has a mixture container for holding the mixture, a rotating screw member or other stirring and transport member disposed inside the mixture container, and a mesh provided in a portion of the bottom panel of the mixture transport path thus formed. A toner refill device for refilling new toner into the mixture container is also provided. Frictional charging of the toner is facilitated by the process whereby the mixture in the mixture container is transported while being agitated by the stirring and transport member. The toner then passes over the top of the mesh, whereupon the toner is discharged onto the electrostatic toner transport substrate through the holes in the mesh. In this arrangement, the toner can be fed to the electrostatic toner transport substrate after being reliably charged by friction with the friction-promoting substance.
However, such new drawbacks as the following occur in this developing device. Specifically, not enough toner can be sifted by the mesh, and the quantity of toner that is fed to the electrostatic toner transport substrate is inadequate.
Therefore, as a result of concentrated investigation of the cause whereby an adequate quantity of toner cannot be sifted, the inventors made such discoveries as the following. Specifically, as a result of strong electrostatic attachment of toner receiving adequate frictional charging to the surface of the friction-promoting particles constituting the main component of the friction-promoting substance in the mixture container, it becomes difficult to separate the toner from that surface. Even if effort is also expended to scrape the toner from the surfaces of the friction-promoting particles with the edge of the mesh holes, the toner is sometimes retained around the periphery of the holes and reattaches to the surfaces of the friction-promoting particles. This phenomenon makes sifting of the toner with a mesh even more difficult.